Lasers (an acronym for light amplification by stimulated emission radiation) are light amplifying devices which produce high intensity pulses of monochromatic light concentrated in a well collimated beam commonly called a laser beam. The laser beam has found wide application in photography, communications, industrial measuring instruments and the like.
Various materials have been used as lasing media. For example, it is known that stimulated emission can be produced in various organic solutions. The first such solutions were of dyes, as reported by Sorokin et al., IBM Journal, Volume II, 130 (March 1967) and, since then, devices which have been used to produce such stimulated radiation have commonly been known as "dye lasers." Some materials which fluoresce or scintillate outside the visible spectrum also have been used. A compilation of materials which have served as the active material in dye lasers is provided in the above cited article of Sorokin et al. and in a review by Kagan et al. in Laser Focus, 26 (September 1968).
U.S. patents which describe dye lasers include U.S. Pat. Nos. 3,541,470; 3,679,995; 3,684,979; 3,818,371; 4,397,023; 4,603,422; and references cited therein.
The characteristics of traditional dye lasers which make them attractive are the possibilities of wide spectral range and tunability at low cost. The laser can be operated anywhere in the visible or into the ultraviolet or infrared ranges simply by changing to a solution which emits electromagnetic radiation at the desired spectral output point.
The output wavelengths of these traditional dye lasers are also tunable, either by varying the concentration of the solution, by varying the solvent, or by introducing a wavelength selective element such as a grating reflector into the optical cavity to control the emission wavelength. Significant spectral narrowing without significant energy reduction is an additional benefit obtained with the use of a grating reflector i.e., line widths less than 1 angstrom can be achieved in contrast to the 50-200 angstrom linewidths which are characteristic of dye laser emissions.
Typical dye lasers have been pumped with Q-switched ruby or glass lasers, or pumping has been accomplished with flashlamps. Pumping has been either in a longitudinal geometry, in which the pumping radiation is colinear with the optical cavity axis and the stimulated radiation, or in a transverse geometry, with the excitation beams at right angles to the optical cavity axis.
Traditional dye lasers have not achieved their full potential because of various disadvantages such as: (1) difficulty in pumping a number of useful materials because of low quantum efficiency or high excited state losses due to singlet-triplet transitions or due to triplet absorptions; (2) low conversion efficiencies, high coupling energy losses, and low repetition rates resulting from thermal effects induced during pumping; and (3) dye circulation problems and other limitations posed by thermal effects.
Several attempts have been made in the prior art to overcome these deficiencies by incorporating a traditional laser dye solution into a solid matrix. For example, Pacheco et al. attempted to solve the deficiencies set forth above by incorporating a laser dye solution into a polymer host such as polymethylmethacrylate, polycarbonate and polystyrene. A Solid-State Flashlamp-Pumped Dye Laser Employing Polymer Hosts, Proceedings of the International Conference on Lasers '87. Polymer hosts, however, are not ideal for dye laser applications because they possess low photostability and low thermal stability.
Another prior art attempt to solve the above-mentioned problem is disclosed in Avnir, The Nature of the Silica Cage as Reflected by Spectral Changes and Enhanced Photostability of Trapped Rhodamine 6G, J. Phys. Chem., Vol. 88, pp. 5956-5959 (1984). Avnir's article discloses the incorporation of Rhodamine 6G dye into a sol-gel derived silica matrix by adding the Rhodamine 6G dye to a silica sol prior to gellation. When a dopant compound is mixed into a sol before gellation, however, gradients are inevitably formed in the final product due to the migration of the dopant to the surface of the product during the subsequent aging and drying stages. Reaction byproducts are thus trapped within the matrix. Further, dye lasers prepared according to this method cannot be subjected to high temperature stabilization treatments without risking the decomposition of the incorporated Rhodamine 6G dye.
In Kuder et al. U.S. Pat. No. 4,878,224, attempt to overcome all of the aforementioned deficiencies by incorporating a solution of a laser dye and a solvent into a glass matrix and then sealing the glass matrix to prevent migration of any of the solution components out of the pores of the matrix. Dye lasers prepared according to Kuder et al., however, may be inefficient because solvent selection is highly critical. Not only must the solvent be compatible with the laser dye while in solution, but it must also possess photostability and thermal stability during lasing. Further, it is the solvent taken in combination with the laser dye, rather than the dye alone, which must provide adequate lasing effects.
Thus, there is a need in the art for dye lasers which have improved photochemical stability and high lasing efficiency. Further, these dye lasers should be convenient to handle as optical parts and should avoid the deficiencies of the prior art.